+/* return the estimated delay based on USB frame counters */
+snd_pcm_uframes_t snd_usb_pcm_delay(struct snd_usb_substream *subs,
+ unsigned int rate)
+{
+ int current_frame_number;
+ int frame_diff;
+ int est_delay;
+
+ current_frame_number = usb_get_current_frame_number(subs->dev);
+ /*
+ * HCD implementations use different widths, use lower 8 bits.
+ * The delay will be managed up to 256ms, which is more than
+ * enough
+ */
+ frame_diff = (current_frame_number - subs->last_frame_number) & 0xff;
+
+ /* Approximation based on number of samples per USB frame (ms),
+ some truncation for 44.1 but the estimate is good enough */
+ est_delay = subs->last_delay - (frame_diff * rate / 1000);
+ if (est_delay < 0)
+ est_delay = 0;
+ return est_delay;
+}
+